Eco-Cement

This page is designed as a first introduction to Eco-Cement, for lay people or students to year 10 or 12.

Introduction

Eco-Cement is a new more environmentally sustainable type of blended cement which
incorporates reactive magnesia[1] and wastes
that is more environmentally sustainable. Eco-Cement used to make permeable concretes
absorbs CO2 and water from the atmosphere to set and harden. It can also be recycled back
to Eco-Cement. Wastes such as fly and bottom ash, slags, plastics, paper glass etc. can also be included
for their physical properties as well as chemical composition without problems
such as delayed reactions.

TecEco plan to make the magnesia[1] that is used in Eco-Cements using solar energy in a new kiln that combines heating
and grinding and captures CO2.

Eco-Cement CO2Release and Capture during Manufacture

Eco-Cement is either carbon neutral except for process emissions which can be very low if non fossil fuel energy is used or negative (resulting in sequestration) if carbon capture occurs during manufacture as planned by TecEco. Given this production scenario Eco-Cement concretes
have the capacity to become a huge carbon sink.

As stated by Fred Pearce in the article on Eco-Cement published in the New
Scientist magazine[2] “There is a way to
make our city streets as green as the Amazon Forest. Almost every aspect of
the built environment from bridges to factories to tower blocks, and from roads
to sea walls, could be turned into structures that soak up carbon dioxide –
the main greenhouse gas behind global warming. All we need to do is change
the way we make cement.”

Making the built environment a repository for recyclable resources (referred
to as waste) as well as a huge carbon sink is an alternative that is both politically
and economically viable.

We want governments to use the power of law to force people to mimic nature and build with carbon to save the planet.

Inspiration

John Harrison got the idea of using carbon and wastes in building materials
from his observations of nature. During earth's geological history, large tonnages
of carbon were put away as limestone and coal by the activity of plants and
animals and approximately 7% of the crust is carbonate sediment. Shellfish build shells from it and trees turn it into their wood. These
same plants and animals wasted nothing, the waste from one was the food or home
of another. John concluded that the answer to the problems of greenhouse gas
and waste was to use them both in building materials. See geomimicry

How do Eco-Cements Work?

Eco-Cements are made by blending reactive magnesia[1] with conventional
hydraulic cements like Portland cement. It is not recommended that large amounts of pozzolan are added to an Eco-Cement as the pozzolan will compete with the carbonation reaction of lime and tend to block the carbonation affect slowing it down. Eco-Cements are environmentally friendly because
in permeable substrates the magnesium oxide will first hydrate using mix water and
then carbonate forming significant amounts of strength giving minerals in a
low alkali matrix. Many different wastes can be used as aggregates and fillers
without reaction problems. The reactive magnesium oxide used in Eco-Cements
is currently made from magnesite (a carbonate compound of magnesium) found in
abundance. In future TecEco hope to make it from abundant magnesium in sea water using the Greensols process in Gaia Engineering.

When added to concrete magnesia[1] hydrates
to magnesium hydroxide, but only in permeable materials like bricks, blocks, pavers
and pervious pavements will it absorb CO2 and carbonate. The greater proportion
of the elongated minerals that form is water and carbon dioxide. These minerals
bond aggregates such as sand and gravel and wastes such as saw dust, slags,
bottom ash, plastics, paper etc. Eco-Cement can include more waste than other hydraulic cements
like Portland cement because it is much less alkaline, reducing the incidence
of delayed reactions that would reduce the strength of the concrete. Portland
cement concretes on the other hand can’t include large amounts of waste
because the alkaline lime that forms causes delayed and disruptive reactions.

Eco-Cement Carbonation

The more magnesia added to Eco-Cement and the more permeable it is, the more
CO2 that is absorbed. The rate of absorption of CO2 varies with the degree of
permeability. Carbonation occurs quickly at first and more slowly towards completion.
A typical Eco-Cement concrete block would be expected to fully carbonate within
a year. Eco-Cement also has the ability to be almost fully recycled back into
cement, should the concrete structure become obsolete. .

1. Magnesite (a compound of magnesium) is heated in a kiln to around 600 to
750 degrees C.

The lower firing temperature of the Tec-Kiln makes it easier to use free energy
such as wind or solar or even waste energy and TecEco plan to make a kiln that
does not use fossil fuels and in which the CO2 gases produced from the magnesium
carbonate as it decomposes is captured and contained for further use or safe
disposal.

2. Grinding in the hot area of the Tec-Kiln will result in increased efficiency.

4. The reactive magnesia[1] (powder) is
added to a pre-determined, but variable amount of hydraulic cement such as Portland
cement, and if desired, supplementary cementitious materials like fly ash.

5. The resulting blended powder is Eco-Cement.

6. When mixed with water and aggregates such as sand, gravel and wastes, Eco-Cement concretes are ready for pouring into concrete, pressing into blocks or other uses.

[1] Reactive magnesia is also variously known as caustic calcined magnesia, caustic magnesia or CCM. The temperature of firing has a greater influence on reactivity than grind size as excess energy goes into lattice energy.

Technical information about reactive magnesia is available in the technical area of our web site.